As a drill used for a cutting process of a workpiece, such as a metal member, a drill described in Japanese Unexamined Patent Publication No. 9-277108 (Patent Document 1) has conventionally been known. The drill described in Patent Document 1 includes a helical flute having an intermediate part in which a flute width gradually increases from a front end of the drill toward a rear end thereof and a helix angle gradually decreases. In the drill described in Patent Document 1, a chip flow distance is short because the helix angle of the helical flute becomes smaller toward the rear end.
Even with the use of the drill described in Patent Document 1, however, there has been the likelihood that chip clogging occurs on the rear end having a relatively large width of the helical flute and a relatively small helix angle. The following can be considered as a cause for this. The force to carry away chips becomes weaker as the helix angle decreases. While a rear end side of the helical flute is made up of a single recessed curved line shape in a cross section orthogonal to a rotation axis. The chips flow along the recessed curved line, and therefore a contact area between the chips and the helical flute increases. Hence, the chip clogging is apt to occur on the rear end side of the helical flute.
The present embodiment has been made in view of the above problem, and aims at providing a drill capable of good discharging chips.